Methods and systems for securing proofs of knowledge for privacy

ABSTRACT

Embodiments described herein relate to securing the privacy of knowledge used to authenticate a user (i.e., Proof of Knowledge (PoK) test(s)). In some embodiments, a client device is operable to receive a first encryption key and encrypted test(s) from a PoK server. The client device also receives a second encryption key from a Relying Party (RP) server. The client device can decrypt the encrypted test(s) by using the first encryption key and the second encryption key to thereby render decrypted test(s). The client device is further operable to obtain answer(s) for the decrypted test(s), send a communication to the PoK server based on the answer(s), and receive a communication from the 
     RP server that authorizes a user of the client device to access service(s) administered by the RP server.

RELATED APPLICATIONS

This application claims the benefit of provisional patent applicationSer. No. 62/035,766, filed Aug. 11, 2014, the disclosure of which ishereby incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to proofs of knowledge and,more particularly, to mechanisms that secure privacy for proofs ofknowledge.

BACKGROUND

Authentication mechanisms include one or more authentication factors tocontrol access to secured services. An authentication mechanism mayrequire a knowledge factor (e.g., a username and a password), anownership factor (e.g., a hardware security token), an inherence factor(e.g., a biometric identifier such as a fingerprint), or combinationsthereof. The first of these is commonly referred to as Proof ofKnowledge (PoK).

Authentication based on PoK includes a provisioning phase (e.g.,enrollment) to define user knowledge, and a use phase to authenticate auser that proves that knowledge. The current paradigm for authenticationbased on PoK is the verification of an identity with a username andpassword. However, there are improved mechanisms for proofs ofknowledge. One such improved mechanism involves the use of picturepasswords that supplement or replace textual passwords, and prove that auser has knowledge of a combination of input actions together with aknown image such as, for example, a still picture, a motion picture withor without sound, or a photograph. Another improved mechanism involvesthe use of cognitive tests, and prove that a user has a certainknowledge and/or cognitive ability. These improved mechanisms generallyrequire two components for the PoK: (1) the test (e.g., the picture forthe picture password, a cognitive testing question, etc.) and (2) theanswer for the test (e.g., the input actions for the picture password,the answer to the cognitive testing question, etc.).

While PoK mechanisms are effective for authenticating users for accessto secured services, they are not very secure or private. Typically, theentity controlling access to the secure services, i.e. the Relying Party(RP), has knowledge of all of the components required for theauthentication, such as the username, password, picture, picturepassword, cognitive test, and answer to the cognitive test.

New systems have emerged to address the issue of security and privacy.One such system is taught in the commonly owned and assignedInternational Application No. PCT/US14/32342 entitled “METHOD AND SYSTEMOF PROVIDING A PICTURE PASSWORD PROOF OF KNOWLEDGE AS A WEB SERVICE,”which is incorporated herein by reference in its entirety. The systemdisclosed therein uses a PoK service that is separate from that of a RP.The PoK service authenticates a user on behalf of the RP. In thissystem, the RP knows the username but not the password, and the PoKservice knows the password but not the username. Security and privacyare improved by fragmenting the knowledge required for authenticationbetween the PoK service and the RP. No single entity, except for theuser, would possess sufficient knowledge to access secured servicesadministered by the RP.

While these new systems that separate username and password improvesecurity and privacy, the PoK service still has the knowledge requiredfor authentication (e.g., the PoK test and corresponding answer) RP.This increases the risk that a third party can obtain and misuse the PoKtesting information in a manner that is detrimental to the user. Assuch, a need exists to further improve the security and privacy inauthentication mechanisms by ensuring that knowledge required forauthentication (e.g., the PoK tests) remains private and unavailable toparties other than the user of a client device.

SUMMARY

Systems and methods disclosed herein relate to securing the privacy ofknowledge used to authenticate a user (e.g., Proof of Knowledge (PoK)tests). In some embodiments, a client device includes a processor(s) andmemory containing instructions executable by the processor(s) wherebythe client device is operable to receive a first encryption key and userdata comprising an encrypted test(s) from a PoK server. The clientdevice also receives a second encryption key from a Relying Party (RP)server. The client device can decrypt the encrypted test(s) by using thefirst encryption key and the second encryption key to thereby render adecrypted test(s). The client device is further operable to obtain ananswer(s) for the decrypted test(s), send a communication to the PoKserver based on the answer(s), and receive a communication from the RPserver that authorizes a user of the client device to access aservice(s) administered by the RP server.

As such, the client device can encrypt and decrypt PoK information byusing an encryption key that the client device generates according to aprocess that is known to the client device and which uses differentencryption keys provided by the RP server and the PoK server. Neitherthe RP server nor the PoK server has access to all the encryption keysnecessary to generate the encryption key used to secure the PoK. Thisreduces the risk that a third party could obtain the test(s) used forPoK and eventually the PoK itself (i.e., the answer(s) to the test(s))to access the user's secured information. Moreover, this reduces therisk that sensitive PoK information (e.g., tests for cognitive testing)could be used in a manner that is detrimental to the user.

In some embodiments, a client device comprises one or more processorsand memory containing instructions executable by the one or moreprocessors. The client device is operable to receive a first encryptionkey and one or more encrypted tests from a PoK server, receive a secondencryption key from a RP server, decrypt the one or more encrypted testsby using the first encryption key and the second encryption key tothereby render one or more decrypted tests, obtain one or more answersfor the one or more decrypted tests, send a communication to the PoKserver based on the one or more answers, and receive a communicationfrom the RP server that authorizes a user of the client device to accessone or more services administered by the RP server.

In some embodiments, in order to decrypt the one or more encryptedtests, the client device is further operable to generate a thirdencryption key from the first encryption key and the second encryptionkey, and decrypt the one or more encrypted tests by using the thirdencryption key to thereby render the one or more decrypted tests.

In some embodiments, the client device is further operable to encryptthe one or more answers by using the third encryption key, and whereinthe communication sent to the PoK server comprises the one or moreencrypted answers.

In some embodiments, the client device is further operable to create acryptographic hash for the one or more answers, and wherein thecommunication sent to the PoK server comprises the cryptographic hashfor the one or more answers.

In some embodiments, in order to generate the third encryption key, theclient device is further operable to generate the third encryption keyby performing one or more logical operations on the first encryption keyand the second encryption key.

In some embodiments, the one or more logical operations are selectedfrom a group consisting of: AND, OR, Exclusive OR (XOR), NOT, Not AND(NAND), Not OR (NOR), and Exclusive NOR (XNOR).

In some embodiments, in order to generate the third encryption key, theclient device is further operable to generate the third encryption keyby taking a split of the first encryption key and the second encryptionkey.

In some embodiments, taking the split of the first encryption key andthe second encryption key comprises performing an XOR logical operationof the first encryption key and the second encryption key.

In some embodiments, the user data is formed as an encrypted BinaryLarge Object (BLOB).

In some embodiments, the encrypted BLOB comprises the one or moreencrypted tests and one or more multimedia objects for the one or moreencrypted tests.

In some embodiments, the one or more multimedia objects comprise animage for a picture password PoK.

In some embodiments, the one or more encrypted tests comprise one ormore cognitive tests, and the one or more cognitive tests comprise theone or more multimedia objects.

Embodiments are also directed to a server computer providing a PoKservice comprising one or more processors and memory containinginstructions executable by the one or more processors. The servercomputer is operable to send a communication to a client devicecomprising a first encryption key and user data comprising one or moreencrypted tests. The one or more encrypted tests are indecipherable tothe server computer. The server computer is further operable to receiveone or more encrypted answers obtained by the client device for the oneor more encrypted tests. The one or more encrypted answers areindecipherable to the server computer. The server computer is furtheroperable to compare the one or more encrypted answers for the one ormore encrypted tests and pre-provisioned encrypted correct answers forthe one or more encrypted tests.

In some embodiments, the one or more encrypted tests were encrypted witha combined key generated from the first encryption key and at least oneother encryption key that is unknown to the server computer.

In some embodiments, the server computer is further operable to send oneor more instructions to the RP server that control access by the user ofthe client device to one or more services administered by the RP server.

In some embodiments, the user data is formed as an encrypted BinaryLarge Object (BLOB), and at least one of the one or more encrypted testscomprise one or more encrypted multimedia objects.

In some embodiments, the one or more multimedia objects comprise animage for a picture password PoK test.

Embodiments are also directed to a RP server comprising one or moreprocessors and memory containing instructions executable by the one ormore processors. The RP server is operable to send a first encryptionkey to a client device and receive a communication from a PoK serverindicating that the client device has been authenticated based on one ormore encrypted tests that were encrypted using the first encryption keyand at least one other encryption key that is unknown to the servercomputer.

In some embodiments, the RP server is further operable to receive acommunication from the PoK server, the communication comprising one ormore instructions for access control by the client device to one or moreservices administered by the RP server, and grant the client deviceaccess to the one or more services administered by the RP server inaccordance with the one or more instructions provided by the PoK server.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 illustrates a Proof of Knowledge (PoK) authentication systemaccording to some embodiments of the present disclosure;

FIGS. 2A and 2B illustrate the operation of the PoK authenticationsystem of FIG. 1 during provisioning of PoK testing according to someembodiments of the present disclosure;

FIGS. 3A and 3B illustrate the operation of the PoK authenticationsystem of FIG. 1 during use of the PoK testing provisioned in FIGS. 2Aand 2B according to some embodiments of the present disclosure;

FIG. 4 is a block diagram of a server computer for a PoK serviceaccording to some embodiments of the present disclosure;

FIG. 5 is a block diagram of a Relying Party (RP) server according tosome embodiments of the present disclosure; and

FIG. 6 is a block diagram of a client device according to someembodiments of the present disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims.

The purpose of terminology used herein is only for describingembodiments and is not intended to limit the disclosure.

As used herein, terms such as “first,” “second,” “third,” and the likedistinguish one element or embodiment from another but should not limitthe element or embodiment. For example, an element can be termed a firstelement or a second element without departing from the scope of thepresent disclosure.

As used herein, the term “client device” refers to a device or apparatusthat includes hardware and/or software that provides a web browser, aclient application operable to communicate using client-serverarchitecture, and/or a client application for retrieving, presenting,and communicating information over a network such as the Internet.

As used herein, the term “Relying Party (RP) server” refers to a deviceor apparatus that provides one or more services accessible by a clientdevice via a network portal (e.g., a website). The services may includeactions and/or information administered by a RP server in accordancewith access controls that require authentication of an identity of auser operating the client device.

As used herein, the term “Proof of Knowledge (PoK) server” refers to adevice or apparatus that includes hardware and/or software to provide aservice (e.g., a password service) used to authenticate a user on behalfof the RP server, where the user is operating a client device.

As used herein, the term “Requesting Party (RQP)” refers to a party thatrequests a PoK service from the PoK server. As such, the RP server mayalso be referred to as a RQP server.

As used herein, the term “AJAX” refers to Asynchronous JAVASCRIPT andXML, any suitable communication technique used to send and receive dataover the Internet from a server, comparable technologies that allow webapplications to send data to and retrieve data from a serverasynchronously (in the background) without interfering with the displayand behavior of the existing page, or any suitable communicationtechnique as understood by persons skilled in the art.

As used herein, the term “picture password” refers to using one or moreknown input actions associated with a known image to provide a passwordfor access to secured information, and/or includes any suitable systemor method for a PoK about an image that a user can readily remember. Asused herein, an image may be, for example, a still picture, a motionpicture with or without sound, or a photograph

As used herein, the term “hash” refers to a cryptographic salted hash, acryptographic salted hash function (e.g., National Institute ofStandards and Technology (NIST) approved SHA256 Password Based KeyDerivation Function (PBKDF)), and/or a derivation of enciphered orencoded data used to authenticate the integrity of correspondinginformation or actions with well-known anti-dictionary attackprotections afforded by cryptographic salting. A hash may also include anumber of hash iterations as suggested by NIST approved PBKDF.

Before describing embodiments of the present disclosure, a descriptionof problems associated with the implementation of existing PoKmechanisms is beneficial.

Improved authentication systems separate the source of privateinformation from the service that authenticates a user seeking to accessthat private information. For example, an RP server may administersecured services that are available to an authenticated user, and a PoKserver may authenticate the user on behalf of the RP server.Authentication requires PoK that may include a user's identity, apicture password, and/or other testing used to assess the mentalcapacity of the user. The knowledge necessary to authenticate the usermay be fragmented between the RP server, the PoK server, and the clientdevice. For example, the RP server may have knowledge of the user'sidentity (e.g., username) but does not have knowledge of the PoK tests.On the other hand, the PoK server has knowledge of the PoK tests butdoes not have knowledge of the user's identity. Instead, the clientdevice operated by the user could have access to all the knowledgenecessary for authenticating that user.

In web login applications and other client-server applications thatprovide separate servers for the RP and the PoK, there is a need toinsure the privacy of an individual user that is logging-in or otherwisebeing permitted access to RP server resources through a client device.

An example of a mechanism to insure the privacy of the individual userincludes factoring a username from a password (whether the username is atext username or any form of token that identified the individual orgroup) from the PoK (whether the PoK is, without limitation, a textpassword, a text Personal Identification Number (PIN), or a picturepassword as disclosed in U.S. Pat. No. 8,813,183 entitled “METHOD ANDSYSTEM FOR PROCESSOR OR WEB LOGON,” which is incorporated herein byreference in its entirety). The RP server knows, or seeks to know, whothe individual or group (the “user”) is (commonly called the identity),while the PoK server knows, or seeks to know, if the individual (i.e.,user), or individual(s) representing the group, has knowledge of asecret or other mental capability (typically, the password). As such, auser's identity may be defined by, for example, a username and/orpassword, and/or the identity may be shared by, and unique to, a groupof users.

Commonly owned and assigned International Application No. PCT/US14/32342discloses that the PoK server need not know the identity of the user toprove knowledge of the user. Furthermore, actual PoK may be revealedonly at the client device. Therefore, the PoK server need not know theactual PoK, but can confirm that the user can perform the PoK correctly(e.g., based on a received cryptographic hash instead of the plaintextPoK).

Factoring separates the RP server's knowledge of who the user is, fromthe PoK server's knowledge of the PoK test, or mental challenge, used toassess the user. A PoK test may include any metric used to assess auser's knowledge or capacity, such as the mental capacity testsdisclosed in U.S. application Ser. No. 14/728,759 entitled “ADVANCEDPROOFS OF KNOWLEDGE FOR THE WEB,” which is incorporated herein byreference in its entirety. Disclosed therein are PoK tests for proof ofmental capacity. A user that does not successfully complete the PoKtests is determined to have diminished mental capacity. As a result, thePoK server sends instructions to the RP server to limit access by theuser to services administered by the RP.

As used herein, a PoK test may be a cognitive test (see, e.g.,en.wikipedia.org/wiki/Cognitive_test) or, equivalently, a mental test asoriginally distinguished by University of Pennsylvania psychologistJames McKeen Cattell (see, e.g.,en.wikipedia.org/wiki/James_McKeen_Cattell) (hereinafter “Cattell”). ThePoK server provides a publishing platform for the vast majority ofcognitive tests that have been developed since Cattell, and any futuremental tests that may be conceived along this testing line of psychologyand related disciplines. Use of cognitive testing can greatly decreasethe risk of fraudulent logins and factoring can protect the user'sprivate knowledge from discovery by the RP server, among other privacyconcerns.

However, it remains that factoring and hashing methods still allow thePoK server to have knowledge of an actual PoK test or challenge. Forexample, in the case of a picture password, the PoK server knows thepicture that may have been uploaded or selected by the user, or in thecase of a text password, the PoK server knows that what is requested ofthe user is a text password (as opposed to, for example and withoutlimitation, a picture password, a PIN, or other test that the clientdevice is instructed to obtain). As such, the PoK server knows thecontent of the PoK test(s) (pictures, texts, etc.) that are used forauthentication.

It would be desirable to have a method and system that permits even moreassurance of user privacy. As such, the present disclosure includesembodiments that provide methods by which even the PoK server does notknow the PoK test(s). In particular, the present disclosure includesembodiments where the PoK test is encrypted on the PoK server such thatthe PoK server cannot fully decrypt the PoK test to have knowledge ofthe test, and the test is equally unavailable to the RP server through asimilar encryption mechanism and/or simply denied by access. Yet, theclient device would have sufficient knowledge to be able to decrypt (orin the case of PoK test creation, encrypt) the PoK test(s).

The disclosed authentication mechanisms have broad applications aspassword PoKs to control access to device resources of all kinds. Forexample, embodiments of the present disclosure can protect againstleakage of passwords and other PoKs that control such resources, andeven the anonymity of the user and a test needed to release access to asecured resource. One such non-limiting example of a physical resourceon a local client machine that can be protected in this way is a“self-encrypting drive” (see, e.g.,en.wikipedia.org/wiki/Hardware-based_full_disk_encryption).

There are many ways to ensure privacy of PoK tests if the user alwaysuses exactly the same instance of a client. For example, if the useralways uses the same machine and the same browser, a cookie (e.g., asmall piece of data sent from a website and stored in a user's webbrowser for use while the user is browsing the website) can hold asecret encryption key. However, if the user can appear from anycompatible client device (e.g., without limitation any machine whetherdesktop or mobile phone) or any client software (e.g., withoutlimitation any Hypertext Transfer Protocol Secure (HTTPS) browser), thenthe problem becomes more difficult. If an additional requirement is thatthe encryption must be completely invisible (transparent) to the user atall times while nevertheless providing the desired privacy protections,then a solution to the problem is even more difficult.

Some embodiments of the present disclosure solve these problems bynoting that the RP server and the PoK server share an anonymous tokenunique to a user identity known by the unique relying party (asdisclosed in the aforementioned PCT/US14/32342, e.g., the anonymoustoken may include a large random number that is unique to the RP serverfor a particular user. Further, the anonymous token may be generated inresponse to a request from the RP server to the PoK server, in a mannerthat is invisible to the user). As detailed below, in some embodiments,the RP server also generates a symmetric encryption key and the PoKserver also generates another symmetric encryption key for this uniqueuser-relying-party pair. These keys are not shared between the twoservers.

Rather, the PoK key is provided when an encrypted Binary Large Object(BLOB) containing the test is provided to the client device. The clientdevice may then be instructed to directly (HTTPS) obtain the RP serverkey and take the split (e.g., Exclusive OR (XOR) the two keys) to createan Effective encryption Key (EK). This EK can then successfully encryptor decrypt the PoK test(s) at the client device.

The request to the RP server for the symmetric encryption key (used forthe split process) may be a one time, time limited request with asession key secret that is shared in this session between the RP serverand the PoK server. This further insures that other parties cannotobtain the RP's key, even if they learn the anonymous user token.

As such, the present disclosure solves the aforementioned problems byproviding systems and methods that secure the PoK used to authenticate auser (e.g., PoK tests). In some embodiments, a client device includesprocessor(s) and memory containing instructions executable by theprocessor(s) whereby the client device is operable to receive a firstencryption key and encrypted test(s) from a PoK server. The clientdevice also receives a second encryption key from a RP server. Theclient device can decrypt the encrypted test(s) by using the firstencryption key and the second encryption key to thereby render decryptedtest(s). The client device is further operable to obtain answer(s) forthe decrypted test(s), send a communication to the PoK server based onthe answer(s), and receive a communication from the RP server thatauthorizes a user of the client device to access service(s) administeredby the RP server.

Accordingly, even the PoK server does not know the PoK test(s) used toauthenticate a user on behalf of the RP server. Instead, the clientdevice encrypts and decrypts PoK test(s) by using an encryption key thatthe client device generates according to a process that is known to theclient device and which uses different encryption keys provided by theRP and the PoK servers. Neither the RP server nor the PoK server haveaccess to all the encryption keys necessary to generate the encryptionkey used to secure the PoK test(s). Moreover, neither the RP server northe PoK server knows the process for generating the encryption key usedto encrypt and decrypt the PoK test(s).

Limiting the exposure of sensitive and private information used toauthenticate a user has several benefits. First, the disclosedembodiments reduce the risk of an insider attack or external hacking ofthe PoK server that would reveal the PoK tests used to authenticateusers. It is particularly easy to see the risk of revealing the privatecontents of a PoK test by anyone with access to the PoK server thatcould obtain and use those private contents in an unauthorized manner.As such, the disclosed embodiments reduce the risk that the PoK serveror a third party could misuse the private content of PoK testing.

Second, the disclosed embodiments reduce the risk that sensitiveinformation used for PoK testing (e.g., cognitive testing) could be usedin a manner that is detrimental to the user. For example, the disclosedembodiments prevent unauthorized use of cognitive testing for purposesother than to authenticate users on behalf of a RP server. Such methodsprevent anyone with authorized or unauthorized access to the PoK serverto assess the cognitive abilities (e.g., mental capacity) of users forunauthorized purposes and/or in a manner that is detrimental to users.As such, the disclosed embodiments reduce the risk that cognitivetesting could be used for purposes other than to authenticate users.

In some embodiments, the PoK tests are encrypted to prevent the PoKserver from viewing the unencrypted PoK tests. Moreover, the PoK serverdoes not have access to an encryption key that could decrypt the PoKtests. The RP server similarly lacks the ability to view the unencryptedPoK tests. Moreover, the RP server may also be denied any access to thePoK tests altogether. Yet the client device would have the encryptionkey to decrypt the encrypted PoK test, and the user of the client devicewould have the knowledge to provide correct answers for the PoK tests.Moreover, the client device would have the ability to encrypt one ormore PoK tests in the case of creating PoK tests. Thus, the private andsensitive information used to authenticate a user is securely isolatedto the client device, as detailed below.

FIG. 1 illustrates a PoK authentication system 10 according to someembodiments of the present disclosure. The PoK authentication system 10(hereinafter sometimes referred to as the “system 10”) may include acombination of one or more servers and/or one or more client devices. Asshown, the system 10 includes client devices 12-1, 12-2, and 12-3(generally referred to herein collectively as client devices 12 andindividually as client device 12), a RQP/RP server 14 (hereafterreferred to as the RP server 14), and a PoK server 16, allinterconnected via a network 18 (e.g., the Internet). In this example,the client devices 12 include a laptop computer 12-1, a desktop computer12-2, and a mobile device 12-3. However, these are only examples. Theclient devices 12 can be any suitable type of device that can beoperated by a user to access the RP server 14.

In some embodiments, the RP server 14 and/or the PoK server 16 canprovide respective services that use one or more distributed serversthat are remote from the client devices 12. In some embodiments, the RPserver 14 and the PoK server 16 are components of a service andcommunicate over a channel separate from the network 18. For example,the client devices 12 may communicate with the RP and PoK servers 14 and16 over the Internet, but the RP and PoK servers 14 and 16 maycommunicate with each other over a separate network.

The RP server 14 provides a portal over the network 18 to display aninterface at the client device 12. The portal may include a website, andthe network 18 may include the Internet. The RP server 14 administerssecured services (e.g., including private information) that can beaccessed by a user via the website rendered on the client device 12.However, the portal provided by the RP server 14 is not limited thereto.For example, the RP server 14 may provide a downloadable application(e.g., an “app”) designed specifically to access the secured servicesover the network 18. For example, the RP server 14 may correspond to aserver operated by a financial institution that administers accountinformation for users to access over the Internet. However, thedisclosed embodiments are not limited to this particular example.

The PoK server 16 may operate to authenticate users of the clientdevices 12 over the network 18 on behalf of the RP server 14. Theprocess performed by the PoK server 16 to authenticate a user isreferred to herein as a process of “PoK testing.” PoK testing mayinclude issuing PoK tests, receiving corresponding answers, renderingresults based on the answers, and providing access control instructionsto the RP server 14 based on the results.

The PoK server 16 provides one or more encrypted PoK tests over thenetwork 18 to the client device 12. The PoK server 16 also provides oneor more encryption keys (hereafter referred to as the “first encryptionkeys”) over the network 18 to the client device 12. The first encryptionkey is unique for each user seeking to access secured servicesadministered by a unique RP such as the RP server 14. Thus, if the PoKserver is used by the same user in the access of secured servicesadministered by two different RP servers, then the PoK server may havetwo unique first encryption keys, one for each of the two different RPservers. The RP server 14 does not have access to any of the firstencryption keys for each user of client devices 12. Instead, the PoKserver 16 and the client devices 12 have access to any first encryptionkeys.

The RP server 14 also provides one or more encryption keys (hereafterreferred to as the “second encryption keys”) over the network 18 to theclient device 12. Similar to the first encryption key, the secondencryption key is unique for each combination of a user and a RP. ThePoK server 16 does not have access to any of the second encryption keysfor each user of the client devices 12. Instead, the RP server 14 andthe client devices 12 have access to any second encryption keys. Assuch, a particular client device 12 has access to both a firstencryption key and a second encryption key for a particular user seekingto access a particular RP with that client device 12.

In some embodiments, the first and second encryption keys may be“symmetric” encryption keys because they are used to both decrypt andencrypt data at the client devices 12. However, in some embodiments, thefirst and second encryption keys are not symmetric. For example, theclient devices 12 may encrypt data using the first and second encryptionkeys but decrypt the same data using encryption keys other than thefirst and second encryption keys, such as private keys in apublic-private key cryptography.

The PoK test(s) may be decrypted at the client device 12 with an EK thatis generated at the client device 12 from the first and secondencryption keys. However, the first and second encryption keys cannotindividually be used to decrypt the PoK test(s). Instead, the EK isgenerated from the first and second encryption keys according to aprocess that is known to the client device 12. As such, the RP server 14and the PoK server 16 do not have access to the EK and knowledge abouthow the EK is generated. Thus, the client device 12 has access to thecombination of the first encryption key, the second encryption key, andthe EK, and has knowledge of the process for generating the EK from thefirst and second encryption keys.

In some embodiments, the process for generating the EK may include aprocess that combines the first and second encryption keys in a uniqueway. In some embodiments, at least a portion of the first encryption keyand at least a portion of the second encryption key may be combined toform the EK. For example, the client device 12 may take a “split” of thefirst and second encryption keys to generate the EK. As such, the firstand second encryption keys are each a “split key.” Two or more splitkeys are added together in some fashion to generate the effective keysuch that any one split key does not have the ability to determine whatthe other split keys are. In other words, any split key cannot deriveany other split key that is used to generate the EK.

In some embodiments, the first and second encryption keys (e.g.,component keys) may have an equivalent cryptographic strength, and theircombination may create an EK that has a cryptographic strength that isdifferent from the first and second encryption keys. For example, addingtwo 16 bit split keys could create a 32 bit EK.

In some embodiments, the first and second encryption keys are processedto generate the EK according to one or more logical operations. Thelogical operation(s) may be selected by the client device 12 from agroup consisting of AND, OR, XOR, NOT, Not AND (NAND), Not OR (NOR), andExclusive NOR (XNOR).

For example, the client device 12 may take a split of the first andsecond encryption keys by performing a bitwise XOR logical operation ofthe first and second encryption keys to generate the EK. Processing thefirst and second encryption keys according to an XOR operation rendersan EK that has the same cryptographic strength as the individual splitkeys (i.e., the first and second encryption keys). However, generationof the EK is not limited thereto.

The EK grants the client device 12 the ability to decrypt the PoKtest(s). In some embodiments, the EK is symmetric such that decryptionand encryption of the PoK test(s) is performed at the client device 12with the same EK. As such, the RP server 14 and the PoK server 16 areunable to generate the EK because each server does not know the otherserver's encryption key and how the client device 12 combines both keysto generate the EK, which is required to decrypt the encrypted PoKtest(s).

For example, the PoK server 16 may provide the client device 12 userdata that includes the first encryption key and an encrypted binarylarge object (BLOB) that contains the PoK test(s). A BLOB, as referredto herein, is a collection of binary data stored as a single entity in adatabase management system. The BLOB may include multimedia objects suchas images or audio, and/or may include binary executable code. Forexample, the BLOB may include a picture for a picture password PoK test.Note that the BLOB is only an example. Any suitable data structure(s)can be used.

The client device 12 may then directly request (via HTTPS) the secondencryption key from the RP server 14 and, for example, take the split(e.g., XOR the two encryption keys) to create the EK. The EK can then beused to successfully decrypt the BLOB including the PoK test(s).

In some embodiments, the request to the RP server 14 for the secondencryption key may be a one time, time limited, request with a sessionkey secret that is shared in a session between the RP server 14 and thePoK server 16. This ensures that other parties cannot obtain the secondencryption key even if the other parties learn of an anonymous usertoken used to establish a session between the client device 12 and thePoK server 16.

The user of the client device 12 is authenticated to access the securedservices administered by the RP server 14 via the website by providingcorrect answers for the PoK test(s). In some embodiments, the clientdevice 12 may use the EK to subsequently encrypt one or morecorresponding answers for the decrypted PoK test(s). In someembodiments, the client device 12 may process the answer(s) to generatea cryptographic hash of the answer(s) without using the EK. Theencrypted answer(s) (or cryptographic hash) are then sent to the PoKserver 16, which uses the encrypted answer(s) (or cryptographic hash) toobtain results for authenticating a user based on the PoK test(s).

The PoK server 16 receives the encrypted answer(s) (or cryptographichash) for the PoK test(s) over the network 18 from the client device 12.The PoK server 16 cannot decrypt the encrypted answer(s) because it doesnot have access to the EK and/or cannot decipher the cryptographic hashof the answer(s). The PoK server 16 compares the encrypted answer(s) (orcryptographic hash) against hash values that represent “correct”answer(s) to determine results of the PoK testing. For example, the PoKserver 16 can compare the encrypted answer(s) received from the clientdevice 12 and the hash values stored at the PoK server 16. A match maybe indicative of a correct answer whereas a mismatch may be indicativeof an incorrect answer. Validation of the encrypted answer(s) by the PoKserver 16 authenticates the user of client device 12.

The results of the PoK testing may include instructions issued by thePoK server 16 that define actions to be taken by the RP server 14 in theevent that the user does not pass one or more of the PoK tests. The userof the client device 12 may then obtain access to the securedinformation administered by the RP server 14 due to the instructionsprovided to the RP server 14 by the PoK server 16, after authenticatingthe user. In some embodiments, the instructions may cause the RP server14 to restrict access to secured services when the PoK server 16determines that a user has diminished mental capacity.

Accordingly, sensitive information used to authenticate a user via PoKtesting remains private. Specifically, the encrypted PoK test(s) andcorresponding encrypted answer(s) are indecipherable to both the PoKserver 16 and the RP server 14 because neither server knows both thefirst and second encryption keys nor how these keys are used to generatethe EK. The term “indecipherable” refers to any form of information thatis incapable of being deciphered without a suitable encryption keyand/or the process for decrypting. As such, indecipherable informationcannot be read or understood without an encryption key to, for example,prevent unauthorized access. Accordingly, the PoK test(s) andcorresponding answer(s) cannot be used for unauthorized purposes. Forexample, the sensitive information used for cognitive testing cannot beused in an unauthorized manner because it is indecipherable to everyoneexcept the user of the client device 12 that has obtained the correctkeys to decrypt and knows how to use the keys to decrypt.

Instead, the RP server 14 and the PoK server 16 will only have abstractknowledge of the PoK testing, such as a level of access that the RPserver 14 should grant an authenticated user based on encrypted answersprovided by the user of the client device 12 in response to encryptedPoK tests provided by the PoK server 16. The encrypted answers andencrypted PoK tests remain indecipherable to anyone other than theclient device 12. Thus, the PoK server 16 and the RP server 14, eitheralone or combined, have insufficient knowledge of a user's privateinformation to enable its misuse.

The system 10 performs processes for provisioning and utilizing the PoKtesting as detailed below. Specifically, FIGS. 2A and 2B show a diagramthat illustrates a process for provisioning the PoK testing. FIGS. 3Aand 3B show a diagram that illustrates a process for using theprovisioned PoK testing. Lastly, FIGS. 4, 5, and 6 are block diagrams ofthe PoK server 16, the RP server 14, and the client device 12,respectively.

FIGS. 2A and 2B show a diagram that illustrates provisioning of PoKtesting according to some embodiments of the present disclosure. Asshown, a client device 12, in response to input received at the clientdevice 12, accesses a network portal (e.g., a website) administered bythe RP server 14 to provision (i.e., setup) PoK testing for accessingone or more services provided by the RP server 14 (step 100). Inresponse, the RP server 14 provides an interface that displays loginoptions (step 102). In some embodiments, the interface enables the userto register a username to establish a new account. In some embodiments,the interface also enables the user to register an initial passwordassociated with the username. In these embodiments, for example, the PoKserver 16 establishes cognitive testing on behalf of the RP server 14,which handles authentication of the username and initial password. Theuser enters the username (and the optional initial password) and mayselect a PoK service to create PoK testing for the new account (step104).

The RP server 14 then sends a request to the PoK server 16 to create anew account that includes PoK testing (step 106). The request does notinclude information that reveals the identity of the user, whichmaintains the anonymity of the user at the PoK server 16. The PoK server16 generates a User Identifier (UID) for the new account and stores theUID in a new record (i.e., the UID record) that may be stored in adatabase of UID records (step 108). As such, the new account for theuser is created at the PoK server 16. The UID can subsequently be usedas an alias for the user when communicating with the PoK server 16. ThePoK server 16 returns the UID to the RP server 14 (step 110). The RPserver 14 stores the UID in a record for the user (step 112). As such,the new account for the user is created at the RP server 14.

The RP server 14 uses the UID to request a login_token from the PoKserver 16 (step 114). In response, the PoK server 16 then returns arandom login_token to the RP server 14 (step 116). The RP server 14provides the login_token in a query string to the client device 12, andredirects the client device 12 to a portal administered by the PoKserver 16 (step 118).

The PoK server 16 then verifies the login_token received by the RPserver 14 (step 120). Upon verification of the login_token, the PoKserver 16 provides an interface for display at the client device 12(step 122). The PoK server 16 also provides data used in conjunctionwith the displayed interface to enable the user of the client device 12to create one or more PoK tests in step 122. In some embodiments, thedata sent to the client device 12 may include the symmetric encryptionkey of the PoK server 16 (i.e., the first encryption key).

The client device 12 then requests the symmetric encryption key of theRP server 14 (e.g., the second encryption key) by using the login_token(step 124). The RP server 14 responds by providing its symmetricencryption key to the client device 12 (step 126). The user of theclient device 12 can then use the interface provided by the PoK server16 to create one or more PoK tests according to a variety of processes(step 128) as detailed above.

As indicated above, the PoK tests may include, for example, a picturefor a picture password or cognitive tests used to assess the mentalcapacity or unique knowledge of the user. As such, the user may beprompted to upload or select a picture for the picture password. Theuser is then prompted to enter a sequence of input actions for thepicture password that corresponds to the “correct answers” to thepicture password test. The combination of the picture and input actionsequence may be temporarily saved locally at the client device 12 as anunencrypted picture password that defines a PoK test and correspondinganswers, respectively.

The user may define PoK testing to include cognitive tests by selectingone or more predefined tests, selecting conditions for activating thetests, providing correct answers for the tests, and designating actionsto be taken by the RP server 14 in the event that the user fails toprovide correct answers during PoK testing. During this initialprovisioning process, the tests, conditions, and actions may betemporarily saved locally at the client device 12 as unencryptedcognitive tests that define the PoK tests. Any and/or all of theunencrypted tests, conditions, and/or actions are discarded after thePoK testing has been provisioned. In other words, the unencrypted PoKtesting information is not retained in memory after being provisioned.Details of the process for creating cognitive tests are omitted here forbrevity. However, the interested reader may refer to U.S. applicationSer. No. 14/728,759, which has been incorporated by reference, fordetails about the process to create the mental capacity tests.

The client device 12 generates the EK using the first encryption key andthe second encryption key (step 130). For example, the client device 12may take the split of both encryption keys by transforming theencryption keys according to a bitwise XOR logical operation. The clientdevice 12 then uses the EK to encrypt the PoK tests stored locally atthe client device 12 to thereby generate encrypted PoK tests (step 132).The client device 12 then sends the encrypted PoK tests to the PoKserver 16 via AJAX without a redirect (step 134). The PoK server 16stores the encrypted PoK tests in association with the UID record forsubsequent use to authenticate the user (step 136). The PoK server 16then redirects the client device 12 back to the website of the RP server14 (step 138).

FIGS. 3A and 3B show a diagram that illustrates a process for utilizingthe PoK testing provisioned in FIGS. 2A and 2B according to someembodiments of the present disclosure. As shown, a user operating theclient device 12 accesses a network portal (e.g., website) administeredby the RP server 14 over the network 18 to request access to one or moresecured services (step 200). For example, the secured services mayinclude providing access to private information such as financialinformation available via the website. In response, the RP server 14provides an interface that displays a login screen (step 202). The userthen enters a username (and the optional initial password) used toidentify the user and select the PoK service to authenticate the user(step 204). In some embodiments, the user enters the username alone toidentify the user (without an initial password), and selects the PoKservice to authenticate the user. The RP server 14 then requests alogin_token from the PoK server 16 using the UID (step 206). The UIDrepresents an alias for the user because the actual username is nevercommunicated to the PoK server 16. Instead, all communications betweenthe RP server 14 and the PoK server 16 use the alias to maintain theuser's anonymity. Only the RP server 14 has knowledge of the username(and in some embodiments, the initial password) used to identify theuser.

The PoK server 16 returns a random login_token to the RP server 14 (step208). The RP server 14 then communicates the login_token in a querystring to the client device 12 and redirects the client device 12 to thePoK server 16 (step 210). The PoK server 16 then verifies the randomlogin_token (step 212). Upon successfully verifying the randomlogin_token, the PoK server 16 provides an interface and the dataassociated with the user for loading by the client device 12 (step 214).

In some embodiments, the data associated with the user may include aBLOB that includes the encrypted PoK tests defined according to theprocess shown in FIGS. 2A and 2B. The data associated with the user mayalso include the symmetric encryption key of the PoK server 16 (i.e.,the first encryption key) and the login_token. The client device 12 usesthe login_token to request the symmetric encryption key of the RP server14 (i.e., the second encryption key) (step 216). In response, the RPserver 14 provides the second encryption key to the client device 12(step 218).

The client device 12 then generates the EK by using the first and secondencryption keys provided separately by the PoK server 16 and the RPserver 14, respectively (step 220). As detailed above, the EK may begenerated according to a variety of processes. As shown, the clientdevice 12 takes the split of both encryption keys transforming theencryption keys according to a bitwise XOR logic operation. The clientdevice 12 uses the EK to decrypt the BLOB containing the encrypted PoKtests provided by the PoK server 16 (step 222). As such, the PoK testsare rendered unencrypted at the client device 12.

The user can then complete the PoK tests at the client device 12 byproviding answers (step 224). For example, the picture for the picturepassword may be displayed at the client device 12. The user then entersa sequence of input actions for a displayed picture of the picturepassword. The input action sequence input by the user may be savedlocally at the client device 12 to define answers for the PoK testsduring the authentication process. If the PoK tests include cognitivetests, the answers to the cognitive tests can be saved locally at theclient device 12 to define answers for the PoK tests during theauthentication process.

The answers can then be encrypted at the client device 12 by using theEK to thereby provide encrypted answers. However, encryption of theanswers is not limited to using the EK. Instead, the client device 12may transform the answers into any cryptographic hash that could be usedby the PoK server 16 to assess the results of the PoK testing. Theencrypted answers and sent back to the PoK server 16 via AJAX with noredirect to the PoK server 16 (step 226).

The PoK server 16 compares the encrypted answers to encrypted “correct”answers obtained during provisioning to determine whether the usersuccessfully passed the PoK test(s) (step 228). The results of thisdetermination may include an authorization token (i.e., “auth_token”)and instructions that are generated for the RP server 14 to controlaccess by the client device 12 to secured services administered by theRP server 14.

The PoK server 16 communicates the auth_token in a query string to theclient device 12 to redirect the client device 12 back to the RP server14 (step 230). The RP server 14 then requests an id_token from the PoKserver 16 by using the auth_token (step 232). The PoK server 16 thenprovides the id_token to the RP server 14 as well as one or moreinstructions determined from the results of the tests (step 234).Lastly, the RP server 14 verifies the user and logs the user in to grantaccess to the one or more secured services administered by the RP server14 (step 236). In some embodiments, access rights to the one or moresecured services is provided in accordance with instructions that defineactions that designate the level of access granted to the user for aparticular service.

FIGS. 4 through 6 are block diagrams of the PoK server 16, the RP server14, and the client device 12, respectively, of the system 10 discussedabove, according to some embodiments of the present disclosure. Asshown, FIG. 4 is a block diagram of the PoK server 16 for providing PoKtesting services according to some embodiments of the presentdisclosure. As illustrated, the PoK server 16 includes one or moreprocessors 20 such as, for example, one or more Central Processing Units(CPUs), Application Specific Integrated Circuits (ASICs), and/or FieldProgrammable Gate Arrays (FPGAs), memory 22, and a network interface 24.In some embodiments, the functionality of the PoK server 16 isimplemented in software stored in the memory 22 for execution by the oneor more processors 20. In some embodiments, the PoK server 16 mayinclude additional components responsible for providing additionalfunctionality, including any of the functionality identified aboveand/or any functionality necessary to support the solutions describedabove.

In some embodiments, a computer program including instructions which,when executed by at least one processor, cause the at least oneprocessor to carry out the functionality of the PoK server 16 accordingto any one of the embodiments described herein as provided. In someembodiments, a carrier containing the aforementioned computer programproduct is provided. The carrier is one of an electronic signal, anoptical signal, a radio signal, or a computer readable storage medium(e.g., a non-transitory computer readable medium such as the memory 22).

FIG. 5 is a block diagram of the RP server 14 according to someembodiments of the present disclosure. As illustrated, the RP server 14includes one or more processors 26 such as, for example, one or moreCPUs, ASICs, and/or FPGAs, memory 28, and a network interface 30. The RPserver 14 also includes an access controller 32 to control access toservices administered by the RP server 14 in accordance withinstructions. As illustrated, the access controller 32 may be embodiedin, for example, one or more ASICs, FPGAs, or any combination ofhardware and/or software components. In some embodiments, thefunctionality of the RP server 14 is implemented in software stored inthe memory 28 for execution by the one or more processors 26. In someembodiments, the RP server 14 may include additional componentsresponsible for providing additional functionality, including any of thefunctionality identified above and/or any functionality necessary tosupport the solutions described above.

In some embodiments, a computer program including instructions which,when executed by at least one processor, cause the at least oneprocessor to carry out the functionality of the RP server 14 accordingto any one of the embodiments described herein as provided. In someembodiments, a carrier containing the aforementioned computer programproduct is provided. The carrier is one of an electronic signal, anoptical signal, a radio signal, or a computer readable storage medium(e.g., a non-transitory computer readable medium such as the memory 28).

FIG. 6 is a block diagram of the client device 12 according to someembodiments of the present disclosure. The client device 12 is shown asan electronic device with a touch-sensitive display (e.g., a smartphoneor a tablet) but may be embodied as any other type of client device. Asshown, the client device 12 includes a control or processing system 34that includes one or more processors 36 (e.g., CPUs, ASICs, and/orFPGAs), a memory controller 38, memory 40 (which may include software 42such as a browser software application), and a peripherals interface 44.

The peripherals interface 44 may communicate with an external port 46,which can provide access to a power system 48. Other components incommunication with the peripherals interface 44 include Radio Frequency(RF) circuitry 50 (e.g., WiFi and/or cellular communications circuitry)and audio circuitry 52 for a speaker 54 and a microphone 56 of theclient device 12. Other components in communication with the peripheralsinterface 44 include one or more accelerometers 58 and other sensors 60.The peripherals interface 44 may communicate with an Input/Output (I/O)subsystem 62, which includes a display controller 64 operable to controla touch-sensitive display system 66, which further includes thetouch-sensitive display of the client device 12. The I/O subsystem 62also includes an optical sensor(s) controller 68 for one or more opticalsensors 70. Lastly, a clock system 72 controls a timer for use by thedisclosed embodiments as detailed above.

Accordingly, FIG. 6 shows components of the client device 12 that enablea user to interface with features of the disclosed embodiments. Theclient device 12 may include other components not shown in FIG. 6, norfurther discussed herein for the sake of brevity. A person skilled inthe art will understand the additional hardware and software includedbut not shown in FIG. 6. For example, the I/O subsystem 62 may includeother components (not shown) to control physical buttons.

In some embodiments, a computer program including instructions which,when executed by at least one processor, cause the at least oneprocessor to carry out the functionality of the client device 12according to any one of the embodiments described herein as provided. Insome embodiments, a carrier containing the aforementioned computerprogram product is provided. The carrier is one of an electronic signal,an optical signal, a radio signal, or a computer readable storage medium(e.g., a non-transitory computer readable medium such as the memory 40).

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. A client device, comprising: one or moreprocessors; and memory containing instructions executable by the one ormore processors whereby the client device is operable to: receive afirst encryption key and user data comprising one or more encryptedtests from a Proof of Knowledge (PoK) server; receive a secondencryption key from a Relying Party (RP) server; decrypt the one or moreencrypted tests by using the first encryption key and the secondencryption key to thereby render one or more decrypted tests; obtain oneor more answers for the one or more decrypted tests; send acommunication to the PoK server based on the one or more answers; andreceive a communication from the RP server that authorizes a user of theclient device to access one or more services administered by the RPserver.
 2. The client device of claim 1 wherein, in order to decrypt theone or more encrypted tests, the client device is further operable to:generate a third encryption key from the first encryption key and thesecond encryption key; and decrypt the one or more encrypted tests byusing the third encryption key to thereby render the one or moredecrypted tests.
 3. The client device of claim 2 wherein the clientdevice is further operable to: encrypt the one or more answers by usingthe third encryption key; and wherein the communication sent to the PoKserver comprises the one or more encrypted answers.
 4. The client deviceof claim 2 wherein the client device is further operable to: create acryptographic hash for the one or more answers; and wherein thecommunication sent to the PoK server comprises the cryptographic hashfor the one or more answers.
 5. The client device of claim 2 wherein, inorder to generate the third encryption key, the client device is furtheroperable to generate the third encryption key by performing one or morelogical operations on the first encryption key and the second encryptionkey.
 6. The client device of claim 5 wherein the one or more logicaloperations are selected from a group consisting of: AND, OR, ExclusiveOR (XOR), NOT, Not AND (NAND), Not OR (NOR), and Exclusive NOR (XNOR).7. The client device of claim 2 wherein, in order to generate the thirdencryption key, the client device is further operable to generate thethird encryption key by taking a split of the first encryption key andthe second encryption key.
 8. The client device of claim 7 whereintaking the split of the first encryption key and the second encryptionkey comprises performing an Exclusive OR (XOR) logical operation of thefirst encryption key and the second encryption key.
 9. The client deviceof claim 1 wherein the user data is formed as an encrypted Binary LargeObject (BLOB).
 10. The client device of claim 9 wherein the encryptedBLOB comprises the one or more encrypted tests and one or moremultimedia objects for the one or more encrypted tests.
 11. The clientdevice of claim 10 wherein the one or more multimedia objects comprisean image for a picture password PoK.
 12. The client device of claim 10wherein the one or more encrypted tests comprise one or more cognitivetests, the one or more cognitive tests comprising the one or moremultimedia objects.
 13. A server computer providing a Proof of Knowledge(PoK) service, comprising: one or more processors; and memory containinginstructions executable by the one or more processors whereby the servercomputer is operable to: send a communication to a client devicecomprising a first encryption key and user data comprising one or moreencrypted tests, the one or more encrypted tests being indecipherable tothe server computer; receive one or more encrypted answers obtained bythe client device for the one or more encrypted tests, the one or moreencrypted answers being indecipherable to the server computer; andcompare the one or more encrypted answers for the one or more encryptedtests and pre-provisioned encrypted correct answers for the one or moreencrypted tests.
 14. The server computer of claim 13 wherein the one ormore encrypted tests are encrypted with a combined key generated fromthe first encryption key and at least one other encryption that isunknown to the server computer.
 15. The server computer of claim 13wherein the server computer is further operable to: send one or moreinstructions to the RP server that control access by the user of theclient device to one or more services administered by the RP server. 16.The server computer of claim 13 wherein the user data is formed as anencrypted Binary Large Object (BLOB), and at least one of the one ormore encrypted tests comprise one or more encrypted multimedia objects.17. The server computer of claim 16 wherein the one or more multimediaobjects comprise an image for a picture password proof of knowledgetest.
 18. A Relying Party (RP) server, comprising: one or moreprocessors; and memory containing instructions executable by the one ormore processors whereby the RP server is operable to: send a firstencryption key to a client device; and receive a communication from aProof of Knowledge (PoK) server indicating that the client device hasbeen authenticated based on one or more encrypted tests that wereencrypted using the first encryption key and at least one otherencryption key that is unknown to the RP server.
 19. The RP server ofclaim 18 wherein the RP server is further operable to: receive thecommunication from the PoK server, the communication comprising one ormore instructions for access control by the client device to one or moreservices administered by the RP server; and grant the client deviceaccess to the one or more services administered by the RP server inaccordance with the one or more instructions provided by the PoK server.